Electrosensitive recording media



I Fm? March 31, 1910 W HpR ET'A L -3,503,855 l ELECTROSENSITIVE Raconn'me MEDIA.

medse t. 14, 1964 INVENTORS FLOYD msa z r- HERBERT E.HELLLUEGE ATTORNEYS United States Patent M 3,503,855 ELECTROSENSITIVE RECORDING MEDIA Floyd W. Shor, Vero Beach, and Herbert E. Hellwege, Winter Park, Fla., assignors to Radiation Incorporated,

Melbourne, Fla., a corporation of Florida Filed Sept. 14, 1964, Ser. No. 396,106 Int. Cl. B41m 5/20, 5/18 US. Cl. 204-2 2 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to recording media and more particularly to electrosensitive recording media sensitive to ultra short duration pulses to provide a graphic display thereof.

Various forms of media have previously been used to provide signal recordings in response to electrical potentials applied by a moving stylus. However, these prior art media in the form of recording charts, blanks, stencils, and the like, have generally been subject to one or more disadvantages which render them unreliable for or inapplicable to the recording or reproduction of many electrical signals. When the signals under investigation are subject to rapid variations, for example pulses of extremely short time base, the medium used must be sufficiently sensitive to accurately and cleanly record with out interfering with the recorder probe and without producing annoying or toxic fumes.

In one known type of electrical recording medium, an electrochemical layer is applied to a paper stock, the layer containing certain chemical compounds which are mixed with binders and whiting agents to provide a color change when stimulated by an electric are from a point probe or stylus. This chemical change is accompanied by a partial burning away of the coating to produce a trace in accordance with the movement of the probe or stylus. Such recording sheets or blanks are generally unresponsive or insensitive to rapid signal changes, i.e. rapid motion of the stylus, because of the necessityof a lengthy exposure to the electric current or are to produce the chemical change. In addition, such electrosensi tive recording media often produce irritating or toxic vapors and doors in conjunction with the partial burning away of the surface coating. Another disadvantage present in most of such prior art recording sheets is the ease with which the surface layer is effaced or marked by handling, and the deterioration of the layer under storage. I

Another type of known electrosensitive recording medium consists of a smooth-surfaced paper stock to which a relatively non-porous plastic layer or plurality of layers is applied. When subjected to electric currents the plastic layer or layers in the vicinity of the arc are removed, exposing the paper stock underneath to provide the desired trace. The adherency of the plastic layer to paper stock is purposely of a temporary nature such that it may easily be removed to provide a stencil by which to reproduce the recording. Such a medium has the disadvantages of relatively expensive production cost, separation of layer and paper base during record ing, and insensitivity to rapid signal variations. In ad- 3,503,855 Patented Mar. 31, 1970 dition, this type of medium is unsuitable for continuous recording since a continuous cut in the plastic layer would result, making it unsuitable for removal from the base for duplicating the recording.

In accordance with the present invention an extremely sensitive electrical recording medium is provided in which an organic semicondnctive coating is adherently applied to a conductive base layer, such as carbon-filled paper stock which contrasts in color'with the dry coating. The semicondnctive coating is rapidly and cleanly removed in response to exposure to electrical potentials between the energized recording stylus and the base layer, through a decomposition and the combustion of the compounds of which the coating is comprised. Special agents incorporated in the coating retard the production of toxic smoke or other irritants which would otherwise accom' pany the reaction, and further provide a surface coating which is not easily elfaced or marked under even extreme conditions of handling or storage, but is rapidly and cleanly vaporized in the presence of an electrical potential. The recording media of the present invention is responsive to pulses of extremely short duration, e.g. microseconds or less, and is thus capable of rapid recording in a positive, reliable, and accurate fashion.

It is therefore a broad object of the present invention to provide an improved electrosensitive recording medium.

It is a more specific object of the present invention to provide a recording medium which is sensitive to ultra short-duration pulses applied to an electrically energized probe to produce an accurate recording of the pulses.

It is another object of this invention to provide an electrosensitive recording medium having an organic semiconductive surface coating adherently applied to a recording base layer.

It is a further object of the present invention to pro vide an electrosensitive recording medium having a special coating which decomposes with a minimum of odor or smoke.

It is another object of the present invention to provide an improved electrosensitive recording medium having a surface coating comprised of relatively inexpensive materials admitting of simple application to a base layer.

It is a still further object of the present invention to provide an electrosensitive recording medium having a surface coating which is not easily marked or removed through handling and which will not deteriorate rapidly even under extreme environmental conditions of storage.

Other objects, features, and attendant advantages will become apparent from a consideration of the following description of a preferred embodiment taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an exaggerated cross sectional view of a recording medium in accordance with the present in vention.

FIGURE 2 is a detailed view of the coating and base layer of FIGURE 1, partially illustrative of the coating constituency; and

FIGURE 3 illustrates the use of an embodiment of the recording medium of the present invention in an exemplary recording structure.

Referring now more particularly to the drawings in which like reference numerals are used to identify like components, FIGURES l and 2 illustrate the relative make-up of a recording sheet in accordance with the present invention. A surface coating or film 15 comprises a colloidal suspension of highly reflective pigment particles 16 in a binder body 18 including a soluble organic compound, the entire coating being oxidized to a semiconductive state. The organic compound tends to coat each of particles 16, as illustrated at 19, to provide relatively constant resistivity. The surface coating 15 is suitably applied to a base layer 20 which may, for example, be a dark-colored carbon-filled conductive paper stock. Application or deposition of the coating 15 to the base layer 20 may be by any suitable technique, for example by spray, roller, or dip methods using Mayer rod, draw knife, air knife, roller coater, or other well-known coating devices. The desired thickness of the overall sheet will determine the thickness dimension of the base layer 20- and, for example, this layer may be several mils in thickness. Layer 20 should be sufiiciently non-porous such that coating 15 may be applied as a single, relatively uniform opaque covering. While other types of paper stock may be used as the base layer, a dark, carbon-filled paper stock is preferred.

FIGURE 2 illustrates the composition of surface coating 15 in greater detail. It is to be understood that FIG- URES 1 and 2 are greatly exaggerated for purposes of clarity. It may be seen that numerous particles of opaque reflective pigment 18 are suspended in a mixture, to be more fully described, including a soluble organic dye precursor, suitable binders and solvents. An alkaline compound in the mixture promotes oxidizing of the coating to the semiconductive state. When subjected to an electrical are, for example between the recorder stylus and the conductive base layer 20, coating 15 decomposes and vaporizes' to expose the base layer to provide a permanent recording on the electrosensitive medium. The chemical structure and thickness of surface coating 15 is, as will be hereinafter described, of such character as to provide extreme sensitivity of the medium to rapid motion of the recorder probe or stylus. Pulses having time duration of 100 microseconds or less and having peak voltages below 300 volts have been accurately and reliably recorded on media in accordance with the present invention.

A typical composition of the surface coating 15 will now be described. A basic formulation of the coating may typically comprise the following component proportions:

60 mg. tetrasodium pyro phosphate (Calgon T) 30 ml. water (distilled) 100 ml. ethylene glycol monoethyl ether (Cellosolve solvent) 30 gm. titanium dioxide 20 ml. polyvinyl acetate (PVA) 600 mg. Lusana Brilliant Blue (dye precursor) The polyvinyl acetate, PVA, is suitable as a. binder being non-flammable and non-irritating in the decomposition process. Further, as opposed to other binders, PVA does not tend to become gummy or to stick to the stylus tip in the presence of the electric arc. Binders which do have such tendency are unsuitable since an accumulation on the stylus will cause electrical shorting between the stylus tip and the conductive base layer 20 and thereby cause inadvertent writing. Anatase titanium dioxide 325 mesh pigment is preferred for providing the opaque hiding properties of coating 15, being superior to rutile Ti because of its good reflectivity and less abrasive character. Anatase TiO further surpasses other pigments of equally fine mesh, for example CaCO 'CaC O M SiO Al Si O BN, M CO Li -CO M C O which may, if desired, be employed with an attendant decrease in reflectivity and a slight loss in hiding property. The necessity of increasing the percentage of solids in the form of pigment in the mixture to overcome these disadvantages would increase the cost of production as well as the electrical resistance of the coating. Therefore, although any of the exemplary materials will suffice the superior characteristics of the anatase titanium dioxide 325 mesh make the latter preferable.

Ethylene glycol monoethyl ether (Cellosolve solvent) is preferred as a thinner and solvent for the dye precursor because it has the characteristics of being nontoxic, evaporating at a much slower rate than other common organic solvents, having a relatively high flash point (approximately 120 F.) and being a relatively inexpensive material. However, other organic solvents may be employed in the mixture if desired. The combination of organic solvent and dye precursor forms a soluble organic precursor which effectively coats each particle of pigment to produce, when oxidized, the semiconductive character of coating '15. Tetrasodium pyro phosphate (Calgon T) is preferably employed to control the viscosity of the mixture, and further to provide alkalinity to aid in oxidation of the soluble organic dye precursor to a semiconductive state. The tetrasodium pyro phosphate may be used in an approximate proportion of 0.2% by weight of TiO The water, in addition to promoting oxidation of the coating, dissolves the Calgon T and produces a leveling action in the mixture to permit smooth, uniform coating of the base layer.

While certain specific proportions by weight of th ingredients of the mixture have been set forth it is to be understood that these proportions are not critical and may be adjusted to suit the particular application involved, for example in terms of thickness of. coating desired and density of background coverage required. Further, any of the exemplary compounds or others of similar characteristics may be used in the coating mixture, if desired, in proportions according to the particular application.

The thickness of coating 15 is of critical importance in those applications where the writing is to occur at pulse durations of microseconds or less and at peak pulse voltages below 30 volts. For such applications the coating should be applied in a single coat of less than approximately 0.5 mil dry thickness and, more preferably, approximately 0.15 to 0.2 ml. The thinnest possible coating is desirable, but present state of the art techniques of application impose a practical limitation of approximately 0.15 to 0.2 mil dry thickness. As previously stated, the coating 15 may be applied by known rod, knife, or roller techniques, for example, to provide such thickness. More than a single semiconductive coating is undesirable, even though a dry thickness of 0.5 mil is not to be exceeded, because the first coat tends to bind the fibers of the base layer 20 together and the second coat tends to cover the stiffened fibers more completely with the result that highest writing quality occurs only in those regions where the larger fibers protrude through the first coating. Thus, a single uniform coating of minimum thickness should be employed.

FIGURE 3""is illustrative of an electrosensitive medium employed in a recorder for graphic display and recording of signals. It is to be understood that the configuration of FIGURE 3 is purely exemplary and that an electrosensitive recording medium in accordance with the present invention may be utilized in any known electrical recorder. The medium 21 is in the form of a suitably marked chart, for example a graph of peak pulse voltage vs. time, suitably placed upon a pair of metal platens 22, 23. The take-up platen may, for example, be driven by a time-synchronous motor (not shown). A stylus 25 is driven by electrical signals to be recorded applied through suitable means (not shown) and is superposed above recording medium 21. An energizing voltage for the stylus, which may be D.C., AC, or pulsating D.C., produces an electric potential which is applied across coating 15 from the stylus or probe tip to base layer 20, the energizing current return path being pro vided through the conducting base layer to a metal platen, for example, 23. The semiconductive coating which has been oxidized to copper phthalocyanine is decomposed and vaporized by the electric arc to expose portions of the base layer 20 therebeneath and thus provides a recording of the signals under investigation. While a single recording is provided by single stylus 25, it is to be understood that the electrosensitive medium may also be used in a multi-signal recorder employin ga-plurality of styli.

In the preparation of the semiconductive coating, the exemplary dye precursor, Lusana Brilliant Blue, dissolved in Cellusolve, methyl alcohol, or other organic solvents, imparts a greenish tint to the mixture. Upon oxidation, through action of the alkaline tetrasodium pyro phosphate and the w ater, the mixture takes on alight blue color, the intensity and depth of color being dependent up on the quantity of precursor used. Thus, the semiconductive coating 15,{;'on base layer 20 provides a pleasing light blue background for the trace produced by the recording process. {The coating flexes'with the base 'paper without cracking, and is relatively unetfected by moisture, sunlight, or ordinary chemical fumes which may be encountered in storage or use. Hence it is not subject to rapid deterioration.

We claim:

1. An electrosensitive recording medium for providing a graphic record in response to electrical potentials in the form of short duration pulses applied thereto, said medium comprising a support sheet of electrically conductive' material,

a pliable electrically semiconductive coating on one major surface of said sheet, said coating being a single layer having a substantially uniform 'dry thickness of less-than 0.5 mil and having a substantially constant electrical resistivity therethrough, said coating comprising a colloidal suspension, in solid phase, of particles of opaque reflecting pigment in a binder, said particles relatively uniformly coated with an oxidized organic dyestutf to provide the semiconducting character of said pliable coating; said coating formed by applying to said sheet a mixture, in the approximate relative percentages by weight, of 16.6% titanium oxide pigment, 0.33% dye precursor, 11% polyvinyl acetate binder, 0.033% tetrasodium pyro phosphate, 55.3% ethylene glycol monoethyl ether solvent, and 16.6% water, said organic dyestuif being a combination of said dye precursor and said solvent, said combination oxidized by said tetrasodium pyrophosphate in the presence of air.

2. An electrosensitive recording sheet comprising an electrically conducting base layer,

a thin electrically semiconducting layer superposed on and in adherent contact with said base layer,

said base layer and said superposed layer being of contrasting color,

said superposed layer having a uniform dry thickness of less than 0.5 mil, and comprising a dry film formed from a mixture of 16.6% titanium dioxide pigment, 0.33 dye precursor, 11% polyvinyl acetate binder, 0.033% tetrasodium pyro phosphate alkaline reducing agent, 55.3% ethylene glycol monoethyl ether solvent, and 16.6% water, in approximate percentages by weight, applied to said sheet in a thickness to conform with said dry thickness, and (dried said mixture) in the presence of air.

References Cited UNITED STATES PATENTS 2,663,656 12/1953 Miller et a1. 11736 2,664,043 12/ 1953 Dalton 2042 XR 2,916,395 12/1959 Owen 117--36.8 3,087,869 4/1963 Hamm et a1 204-2 3,108,896 10/1963 Owen 11736.8 3,122,448 2/ 1964 Hills et al 117-211 3,167,444 1/1965 Baumann et a1. 11736.8 3,216,855 11/1965 Ellison 117216 3,255,039 6/1966 Dalton 117-215 JOHN H. MACK, Primary Examiner w. B. VANSISE, Assistant Examiner US. Cl. X.R. 11736.8, 215, 216 

